Re: [PATCH v4 07/11] pack-objects: refer to delta objects by index instead of pointer

Nguyễn Thái Ngọc Duy  [off-list ref] writes:

These delta pointers always point to elements in the objects[] array
in packing_data struct. We can only hold maximum 4GB of those objects

4GB, as in "number of bytes"?  Or "We can hold 4 billion or so of
those objects"?

because the array length, nr_objects, is uint32_t. We could use
uint32_t indexes to address these elements instead of pointers. On
64-bit architecture (8 bytes per pointer) this would save 4 bytes per
pointer.

Convert these delta pointers to indexes. Since we need to handle NULL
pointers as well, the index is shifted by one [1].

[1] This means we can only index 2^32-2 objects even though nr_objects
    could contain 2^32-1 objects. It should not be a problem in
    practice because when we grow objects[], nr_alloc would probably
    blow up long before nr_objects hits the wall.